1. Field of the Invention
This invention relates to a tape wire for use mainly on automotive wiring harness which has an increased conductor cross section and an improved allowable current and also relates to the method of manufacturing such a tape wire.
2. Description of the Prior Art
The tape wires were developed mainly for wiring in commercial equipment. Most of such tape wires consist of signal conductors, each about 0.01 mm.sup.2 in cross section, held and bonded between insulating tapes from both sides. Each conductor is about 0.1 mm thick. When this tape wire is to be used in power circuits of automotive wiring harness, a conductor of at least 1.25 mm.sup.2 in cross section is required, considering the allowable currents. With conventional conductors about 0.1 mm thick, however, the conductor width becomes as large as more than 12.5 mm, reducing the circuit integrity. If it is attempted to reduce the wire width by increasing the conductor thickness, a conventional manufacturing method may cause an undesired situation. That is, as shown in FIG. 6, when a conductor a is bonded with insulating tapes b, a gap c where there is no bonding agent may be formed at the side edge portion a.sub.1 of the conductor. Possible ingress of water into such gaps will result in corrosion and other electrically detrimental conditions.
To circumvent this problem, a tape wire has been proposed (Japanese Utility Model Preliminary Publication No. Showa 62-74709) in which the side edge of the conductor a is worked into a knife edge a.sub.2, as shown in FIG. 7, to prevent formation of the air gap at the side edge of the conductor.
However, forming the side edge of the conductor a into a knife edge a.sub.2 deteriorates productivity, increasing cost.
Another tape wire is also proposed (Japanese Utility Model Preliminary Publication No. Heisei 3-94722), in which an insulating member d virtually as thick as the conductor a is interposed between the conductors a to make the tape wire uniform in thickness as shown in FIG. 8 so that the pressing force with which the insulating tape b is bonded is equal over the entire surface.
However, when the tape wire of FIG. 8 is used in automobiles and repetitively subjected to lateral bending and friction during installation and to vibrations during operation of the car, stress concentrates at the edge portion a.sub.3 of the conductor a, breaking the insulating tape b and exposing the conductor a, as shown in FIG. 9. This construction has low durability.
When the cross section of the interposed insulating member d is made closer in shape to a square to reduce the intervals between the conductors a, it becomes difficult to arrange them orderly, significantly degrading the productivity in the manufacturing process.